The present invention generally relates to an intramedullary nail system for reducing and fixing bone portions across a fracture therebetween providing a means of fixation through the use of tangs, screws or a combination of both.
In its most basic construct bones are formed of a relatively soft, spongy cancellous material surrounded by a much harder cortex. The cancellous bone yields under relatively low loading, while the much more dense cortical bone supports much higher loading. There have been a number of techniques used historically for treatment of fractures of the femur, humerus or tibia (referred to as the long bones). In early parts of this century, patients were merely placed in bed-or in traction for prolonged periods, frequently resulting in deformity or death.
In the 1930s, the Smith-Peterson nail was introduced. This device was inserted into the intramedullary canal of the femur resulting in immediate fixation of hip fractures, early mobilization of the patient, and a lower morbidity and mortality. A number of nails have been introduced for intramedullary fracture fixation of long bones, including the Jewett Nail and Enders Nail.
Later intramedullary nails increased in diameter and surgeons/inventors began to experiment with cross section designs and radii of curvature along the nail""s length. Since the femur curves slightly along its length, it was preferred that the nails have a similar long radius of curvature of, for example 50 inches. These nails were inserted down the entire length of the femoral canal to provide a basis for the construct. Fixation methods for certain types of fractures often required the nail to bear a portion of the patient""s weight during the recovery period. Threaded wires, standard bone screws or cannulated bone screws were then inserted through or along side the nail and into the outer cortex to provide enough fixation and rotational stability to bear weight during recovery.
As these intramedullary nails became longer other problems occurred. In longer nails the distal tip of the nail tends to rotate out of plane which forces the surgeon to target the distal screw holes using fluoroscopy by a method commonly known as xe2x80x9cfree-handingxe2x80x9d. Under this technique the surgeon utilizes fluoroscopic images in search of perfectly circular screw holes. Once found a mark is made on the patient, an incision is made and a pathway cleared to the cortical bone. A dimple is placed on the lateral cortex to reduce xe2x80x9cdrill walkingxe2x80x9d and the hole is then drilled and a screw inserted. Adjustments to this procedure are quite common; even to those skilled in the art of free handing.
Numerous patents, both domestic and foreign, have been granted citing devices which reduce the complications associated with distal screw targeting. The methods of accomplishing this task are varied, but the results are the same: Very few of the ideas have been developed and marketed as useful products. The majority of surgeons still return to free handing because there is a perceived time savings. Therefore, external methods for distal screw targeting have not gained favor.
Newer devices and inventions explored additions to the nail to eliminate the need to locate the distal screw holes and improve the fixation. These newer devices are commonly classified as xe2x80x9cexpanding devicesxe2x80x9d and expand in size after placement to fill the intramedullary cavity. In the early 1980s, the Brooker-Wills Nail came on the scene and others soon followed. Freedland, U.S. Pat. Nos. 4,632,101, 4,862,883 and 4,721,103, Chemello, U.S. Pat. No. 6,077,264, and Davis, U.S. Pat. No. 5,057,103, describe methods of fixation which provide points which contact the internal cortical wall. In these patents a mechanism is actuated deploying arms or anchor blades through the cancellous bone to contact the inner cortical wall. These methods are complex and the arms are difficult to retract should the nail or lag screw assembly requires extraction. These arms do not deploy through the cortical bone.
Other expanding devices provide surface contact with the internal cortical wall resulting in a wedge effect. Kurth, U.S. Pat. No. 4,590,930, Raftopoulos, U.S. Pat. No. 4,453,539, and Aginski, U.S. Pat. No. 4,236,512, among others have described mechanisms which deploy or expand with a molly bolt concept. These methods are complex and the devices are difficult to retract should the nail require extraction. Neither do these devices deploy through the cortical bone.
Bolesky, U.S. Pat. No. 4,275,717, was the first to discuss engagement within the cortical wall. However, Bolesky""s invention does not address controlled penetration into the wall and required permanent implantation of the actuation rod. In addition, Bolesky does not address the fundamental problem of the actuation rod""s protrusion extramedullarly into the surrounding musculature.
In U.S. Pat. Nos. 5,976,139 and 6,183,474B1, Bramlet et al describe a surgical anchor which has deployable tangs. These tangs are simple in design, internally positioned, yet easily deployed into, and if desired through, cortical bone providing improved purchase for compression of a proximal femur fracture, especially in osteogenic bone. These tangs are just as easily retracted should the device require explantation.
The intramedullary nail system according to this invention is especially suitable for installation within the medullary canal of a fractured long bone, such as a femur, humerus, or tibia and subsequently interlocking the nail and bone thereby preventing axial translation and axial rotation.
The intramedullary nail is, preferably, roughly circular in cross section and elongated although any number of cross sectional shapes may be used. The nail is, preferably, cannulated and anatomically curved to fit the shape of a bone.
The cannulated intramedullary nail allows passage of one or more anchoring tang assemblies. These anchoring tang assemblies are inserted from the proximal end and telescoped through the axial bore towards the distal end by a insertion/deployment/retraction instrument. An alternate embodiment has a retracted tang mounted on a tang assembly that is permanently placed within the intramedullary nail and is deployed and retracted by the above mentioned instrument.
The proximal end of the nail contains a securing arrangement for a tool for driving and extracting the nail. The tool advantageously cooperates with a slot in the proximal end of the nail so that the desired angular disposition of the nail is indicated and easily maintained during insertion of the nail.
When the intramedullary nail is placed into position, the anchoring tang assembly is actuated to deploy the tangs outwardly from their stowed position through the portals and into the cortical bone. The interlocking of the intramedullary nail to the cortical shell of the long bone may be achieved, at least once, using at least one screw or at least one tang assembly. In the preferred embodiment, several tang assemblies would be positioned longitudinally within the nail based on the fracture location and the surgeon""s assessment for proper fixation. The tangs are deployed to any desired position thereby achieving a desired fixation and rotation prevention based upon the quality of the bone. Should the system require additional load carrying capability, cortical screws may be placed to further secure the nail with the surrounding bone.
The anchoring tang assembly contains arcuate shaped tangs that are permanently attached to the tang assembly body. These tangs are initially formed into a prescribed position for storage. As the assembly is actuated, the tangs deploy and are formed into their final shape through interaction with the portal in the nail.
The end cap preferably contains a coating of ultra-high molecular weight polyethylene (UHMWPE) within the threads. This provides constant positive engagement between the end cap external threads and the intramedullary nail internal threads preventing loosening of the end cap due to bodily forces.
Should the situation arise in which the surgeon requires removal of the intramedullary system, the tangs are completely reversible. The end cap is removed and the tang assembly insertion/deployment/retraction instrument is inserted through the axial bore. When the first tang assembly is encountered, a force is exerted on the instrument against the tang body causing the body to move longitudinally resulting in the tangs engaging the portal and pulling away from the bone and returning inside the nail. Once the tangs are completely inside the axial bore, the tang assembly is free to slide within the intramedullary nail. Force is continually applied, to the instrument, telescoping the instrument and tang assembly further along the nail until another tang assembly is encountered. The first tang assembly will xe2x80x9cnestxe2x80x9d with the second tang assembly. Upon continued pressure, the entire assemblage telescopes through the axial bore until the last tang assembly has been retracted and rests against the bottom of the axial bore of the intramedullary nail. The nail can then be extracted from the bone.
In one embodiment of the present invention, the intramedullary nail system is combined into a kit which includes several intramedullary nails of differing lengths and/or diameters and/or shapes, each having an axial bore, radial bores and portals which allow passage of different sized locking screws and anchoring tangs through the nails into the surrounding bone. The intramedullary nails have a distal end and a proximal end with internal threads in the proximal end. Several like-sized end caps are provided in the kit, each with external threads to cooperate with the internal threads in the proximal ends of the nails. Different sized tang assemblies are in the kit for selective telescoping movement through like-sized axial bores of the several nails. The tang assemblies may differ in diameter and/or in the length of the tangs carried by the tang assemblies. Also in the kit are several different sized cortical screws for use in conjunction with the nails. One or more insertion/deployment/retraction instruments are provided in the kit to manipulate the tang assemblies in the axial bore of a nail to deploy the tangs through the portals into a bone. The instrument is of a length that it may be manipulated at the proximal end of the nail to deploy or retract tangs at the distal end of the nail. The kit allows the surgeon flexibility in selecting the proper nail system for the fracture presented by the patient. The entire kit may be sterilized and presented in the operating room or some choices may be made earlier as to the elements to be used in a particular situation.
Finally, once the intramedullary nail is locked into the bone a condition known as stress shielding is typically inherent in the bone. As the bone heals these stresses need to be relieved. The bone can heal in a pre-stressed condition and refracture at a later date or the nail rotates with respect to the bone and repeated loading causes screw failure.
Clearly a need exists for a system that offers the ease of insertion and superior performance of existing intramedullary nails while minimizing the surgical insult to the human body and eliminates the need for distal screw targeting. Such a system would include a simple, effective and controllable fixation device which allows greater purchase of the bony fragments, provides a means of rotational stability in the femoral shaft, and offers to minimize, if not eliminate the need for additional distal incisions to locate and place locking screws. This system would be designed to allow the surgeon a choice of penetration distance within the femoral shaft and fixation based upon the injuries presented and the desired level of treatment. Finally, this system would allow explantation to occur as easily as implantation.